A friend of mine had the tricky job of explaning remembrance day to her four year old daughter recently. This involved explaning what guns were (girls are apparently less interested in high calibre firearms at that age than boys). To quote my friend, a gun is a a machine you hold in your hands that makes pieces of metal fly towards other people at high speeds. I think my friend missed out the bit about what happens when aforementioned high speed projectiles reach those other people, because her daughter’s response was “Why would anyone want to do that?”.
To be honest I can’t think of an answer to that question. At least, I can’t think of an answer that would please a four year old.